Re: On Memory
From: Barry Margolin (barmar_at_alum.mit.edu)
Date: 09/25/04
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Date: Fri, 24 Sep 2004 20:05:55 -0400
In article <3bfe502e.0409240843.4c24de7e@posting.google.com>,
maitaimaker@gmail.com (Maitaimaker) wrote:
> No, I don't care about where you were last thursday at 8:53PM. I'm talking
> about physical and virtual memory in our unix world. For quite some time
> you'd look at virtual memory to be somewhere in the neighborhood of twice
> physical. These days where physical memory can easily range into multi
> gigs, is that necessarily practical or even useful? Has anyone done any
> research as to what a new standard should be, or does the old one work
> find even still? Lastly, is there a practical upper limit to virtual
> memory? I'd imagine that at some point you hit diminishing returns, due to
> bus speed, seek times, etc. Am I thinking wrong on this? Enquiring minds
> want to know...thanks for your input.
The old rule of thumb was based on the assumption that most
organizations couldn't afford enough physical memory to hold all
processes' working sets. The recommendation was typically described as
VM should be twice physical memory, but what I think was really meant
was that you should have enough RAM for at least half your typical
working set, in order to avoid thrashing. But if you can afford more
RAM, it can hardly ever hurt.
The basic idea is that the VM size specifies how many processes can run,
and the RAM size specifies how fast they'll run when they're all
competing for memory.
-- Barry Margolin, barmar@alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me ***
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